The object of this proposal is to study the mechanisms of oncogenesis in ovine pulmonary carcinoma (OPC), a naturally occurring lung cancer of sheep. OPC is caused by a retrovirus known as Jaagsiekte sheep retrovirus (JSRV). OPC has strikingly similarities with human bronchioalveolar carcinoma (BAC), a lung tumor that is only weakly associated with cigarette smoking and now represents a quarter of all lung cancers in the U.S. Animal models of retrovirus-induced neoplams have given insight into the genetic basis of cancer and have led to the discovery of oncogenes. Thus, OPC is a unique model to investigate lung carcinogenesis and the only viral-induced pulmonary neoplasm in domestic animals. The causal association between JSRV and OPC has been demonstrated by the isolation of an infectious and pathogenic molecular clone (JSRV2 1) but the mechanisms used by JSRV to induce cell transformation are not known and are the object of this proposal. The expression of the JSRV envelope is sufficient to induce transformation of rodent fibroblasts in classical transformation assays. These results suggest a novel mechanism in retroviral-induced oncogenesis. Preliminary results show that the antiapoptotic cell signaling pathway initiated by phosphoinositide-3 kinase (Pl-3K) is constitutively active in JSRV-transformed NIH3T3 but not in the parental cell line. In addition, replication competent JSRV mutants that have lost the ability to transform rodent fibroblasts in vitro have been obtained. These mutants have a single a single point mutation in a tyrosine of the cytoplasmic tail of the transmembrane region of the JSRV envelope altering a putative docking site for PI-3K. These results create an exciting rationale for this proposal whose aim is to dissect and understand the mechanisms of JSRV-induced carcinogenesis both in vitro and in vivo in its natural host. Aim 1 is to dissect the signal transduction pathway initiated by the JSRV envelope in rodent fibroblasts and in cell lines obtained from naturally occurring OPC tumor. However, the mechanisms of carcinogenesis in vivo are likely to be more complex that those followed by JSRV to transform immortalized cell lines. In Aim 2, newborn lambs will be inoculated with JSRV-based vectors and mutants that will determine whether the expression of the viral envelope and the activation of the PI-3K signaling cascade are necessary and/or sufficient to induce lung carcinogenesis. Aim 3 is to look for further mechanisms contributing to oncogenesis in OPC by analyzing the viral insertion sites in naturally occurring OPC-cases. The completion of these experiments will clarify the molecular mechanisms of JSRV-induced pulmonary carcinogenesis and might furnish an intellectual framework to unravel the pathogenesis of some forms of human lung cancer.